builddeb: fix cross-building to arm64 producing host-arch debs

Both Debian and kernel archs are "arm64" but UTS_MACHINE and gcc say
"aarch64".  Recognizing just the latter should be enough but let's
accept both in case something regresses again or an user sets
UTS_MACHINE=arm64.

Regressed in cfa88c79: arm64: Set UTS_MACHINE in the Makefile.
Signed-off-by: Adam Borowski <kilobyte@angband.pl>
Acked-by: Riku Voipio <riku.voipio@linaro.org>
Signed-off-by: Michal Marek <mmarek@suse.com>

scripts/package/builddeb

@@ -51,7 +51,7 @@ set_debarch() {
 		debarch=hppa ;;
 	mips*)
 		debarch=mips$(grep -q CPU_LITTLE_ENDIAN=y $KCONFIG_CONFIG && echo el || true) ;;
-	arm64)
+	aarch64|arm64)
 		debarch=arm64 ;;
 	arm*)
 		if grep -q CONFIG_AEABI=y $KCONFIG_CONFIG; then